Project Summary ? Kim While current anti-HIV therapeutic agents contribute to the effective suppression of HIV-1 in patients, actual choices for long-term treatment is rather limited due to viral escape, cross-resistance, and toxicity, demanding discovery of newer and safer classes of anti-HIV agents. HIV-1 requires various host intracellular factors for completing its life cycle and pathogenesis. Targeting the interactions between viral proteins and these host intracellular factors has been extensively explored as a potential anti-viral discovery path while anti-HIV agents targeting the viral interactions with intracellular factors are currently limited. A recent collaborative work between Emory Center for Drug Discovery (CDD) and ST Pharm, CO, LTD identified a highly potent anti-HIV compound with outstanding in vitro and animal toxicity and pharmacokinetics, STP03-0404: STP03-0404 was originally identified as an anti-HIV hit by the random anti- HIV compound screening operation of ST Pharm that employed a series of chemical scaffold libraries uniquely developed by ST Pharm. The EC50 values of STP03-0404 determined by Southern Research Institute (SRI, Frederick, MD) with human PBMCs and various clinical HIV-1 isolates, and also independently determined by Emory CDD are in pico-molar ranges. Furthermore, the tissue culture based therapeutic index of STP03-0404 was 40,000-1,000,000, and the preclinical animal investigations with rats and dogs demonstrated its outstanding safety and excellent pharmacokinetics. Excitingly, our extensive computational structure-based search efforts and initial X-ray crystallographic analysis proposed that STP03-0404 targets the LEDGF/p75 binding pocket at the interface between two monomers of HIV-1 integrase (IN) and therefore this compound works as an allosteric integrase inhibitor (ALLINI). Importantly, we found that STP03-0404 displays up to ~ 1,000 times more effective anti-HIV-1 activity than previously reported ALLINIs. Furthermore, STP03-0404 effectively inhibits clinical HIV-1 strains with resistance to catalytic site integrase inhibitors such as Raltegravir. Therefore, in this application, we will structurally and chemically investigate STP03-0404 as a highly potent and safe ALLINI platform. For these investigations, we propose to employ a series of in-depth biochemical, structural biology, virological/genetic approaches as well as medicinal chemistry/chemical optimization designed for new derivatives of STP03-0404 with enhanced genetic barrier to resistance. Ultimate goal of this application is to meet the current demand for newer and safer anti-HIV agents by pre-clinically investigating STP03-0404 as a novel, potent and safe anti-HIV drug discovery platform.